The challenge was to build a motor-powered machine that would move the most green polystyrene "sand" into a hole in 30 seconds, and Prof. Erik Antonsson's class of 24 tried just about everything.

There was a machine that flung the stuff like a side-armed pitcher. There was one that blew it like a snow blower. There were scoopers, pushers and miniature forklifts. And there were predator machines that tried to disable the opposition.

But Zitola's little low-to-the-ground purple gadget with the big plow kept scooping and scooping, like a young St. Bernard eating kibbles.

Finally, in the deciding match, Zitola's machine went mano a mano against Michael Smith's miniature bulldozer and won effortlessly. "The principle is to keep it simple and make it work right," said the unflappable Zitola, a senior from Massachusetts who is majoring in mechanical engineering and geology. "And don't stress."

This may all have seemed like a frivolous exercise, Antonsson said, but it confronted his students, some of whom aspire to careers designing robots and vehicles, with a strong dose of reality. "The idea is to give the students experience in designing and building something that actually works," he said.

The contest constitutes Antonsson's final exam for what Caltech students call "ME72," the 10-week design course.

At the start of the course, each student had been given a design assignment and a "bag of junk," an assortment of more than 100 pieces of hardware, including two 24-volt motors. These were their building materials.

"A good design works consistently, it satisfies the objective, it works under various conditions and it confronts all of the exigencies of the real world," said Antonsson, a slim man with a bushy mustache, who is one of Caltech's most popular professors.

Some students spent more than 200 hours constructing their gadgets.

The final test was played out on a pair of 8-by-4-foot playing fields before a raucous audience of about 700. The contestants connected their machines to power "umbilicals," two dangling wires with hookups like those in a telephone jack, and went one on one. Stretched across the middle of each field was a trough of granular polystyrene. The challenge was to move the stuff quickly into a pair of "drains" without stumbling into the hole or becoming mired.

The contestant who put the most material in the drain in 30 seconds won a round. Two losses resulted in elimination.

Throwing an element of unpredictability into the contest was a group of aggressors--machines that could not move a lot of material but which could disrupt their opponents. "In the last couple of days, a lot of new strategies have surfaced," Antonsson said.

Before the contest, Zitola and others warily circled Matt Johnson's ingenious little catapult. Johnson's strategy was to sail a plastic "plug" across the field, using rubber bands like a slingshot, and block his opponent's drain. If it was successful, the plug would keep the opponent from accumulating any sand, and Johnson could push a grain or two into his drain and win.

But the contraption did not work. Johnson got the plug in his opponent's drain but without fully covering the hole. He was eliminated in two matches. Adrienne Miller, however, shot across the sand trough and dropped a plug, perfectly covering the drain of Brian Duchovnay, foiling his green zebra-striped bulldozer. But it only worked perfectly once.

After all the cheers, Zitola cradled his little machine like a baby and showed it off. Those knobby tracks that propelled the machine over the insidiously shifty polystyrene were made in his own silicone mold with rubber backed by nylon. "It's the same principle as the steel-belted tire," Zitola said.

There was some sentiment at the end that the sand that the machines competed on was different from the substance that the students had practiced on. "This stuff was easier to drive on," said Michael Klitzke, whose snow-blower-like machine was eliminated early. "That's why some of us went to rotary designs."

Antonsson was unsympathetic. "These perfectly angelic engineers," he said, "when they're given a job like this, they turn into lawyers."